documentary (adj.)

1788, "pertaining to or derived from documents," from document (n.) + -ary. Meaning "factual, meant to provide a record of something" is by 1921, originally in reference to film, from French film documentaire (by 1919). The noun (short for documentary film) is attested by 1935.

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Definitions of documentary from WordNet
documentary (adj.)
relating to or consisting of or derived from documents;
Synonyms: documental
documentary (adj.)
(of film, television, radio, or photography) depicting a real-life event using images or interviews with people involved in the event;
documentary (n.)
a film or TV program presenting the facts about a person or event;
Synonyms: docudrama / documentary film / infotainment